The present invention relates to a disc player having a single turntable and a single drive motor which can receive and rotate various types of information carrier discs having different diameters, such as digital audio discs manufactured according to the compact disc digital audio system standard and video discs manufactured according to the laser vision standard.
In the prior art, Japanese Utility Model Preliminary Publication No. sho 60-106280 discloses an example of a disc player which can receive several types of information carrier discs having different diameters. As shown in FIG. 1, this conventional disc player has a chassis 1 on which a bracket 2 is attached. A mount segment 3 is pivotally connected at its corner 3a to the bracket 2 via a pin 4 for the movement in the direction indicated by the double-headed arrow (E)(F). This mount segment 3 is provided at that portion of its arcuate edge near the corner 3b, with a drive motor 5 for rotating a disc having a large diameter, and at that portion of its arcuate edge near the corner 3c, with another drive motor 6 for rotating a disc having a relatively small diameter. A turntable 7 for supporting the larger disc is attached to the rotation shaft of the drive motor 5, and a turntable 8 for supporting the smaller disc is fixed to the rotation shaft of the drive motor 6. The mount segment 3 has an arcuate rack 9 formed along its arcuate edge. With this rack 9, a pinion 10 is meshed. The pinion 10 is born by the casing (not shown) of the player and connected to another motor supported by the chassis 1. When the pinion 10 is rotated, the mount segment 3 is pivoted in the direction (E) or (F). As shown in FIG. 1, when the mount segment 3 is pivoted in the direction (E) to its left most position, a pin 11 on the segment 3 contacts with the stopper 12 on the chassis 1, and the axis of the turntable 7 coincides with a vertical base line 13. On the other hand, when the mount segment is pivoted in the direction (F) to its right most position, another pin 14 on the segment 3 contacts with another stopper (not shown) on the chassis 1, and the axis of the turntable 8 coincides with the base line 13. When the axis of either of the turntables 7 and 8 coincides with the base line 13, the turntable 7 or 8 is ready to receive and rotate the disc. That is, in order to receive the discs having different diameters, this disc player has the two turntables 7 and 8 for supporting the discs, the two drive motors 5 and 6 for rotating the turntables 7 and 8 respectively, and the rack 9 and the others, i.e., a mechanism for switching the turntables 7 and 8. This results in a costly, over sized disc player.
In order to make the above-described conventional disc player simple, compact and less costly, one of the turntables 7 and 8, and one of the drive motors 5 and 6 should be omitted. However, in designing a disc player having a single turntable and a single drive motor and still capable of playing discs having different diameters, there arises many problems because of the difference in the manufacturing standards of the various discs.
For example, there arises a problem with the drive motor in creating a disc player for both audio and video discs. The audio disc has an outer diameter of 120 mm, a thickness of 1.2 mm and a weight of 20 g. The video disc has an outer diameter of 300 mm, a thickness of 2.5 mm and a weight of 200 g. The digital audio disc must be driven at a revolution of 200 to 500 rpm, and the video disc, in this case the standard video disc of the constant angular velocity type, must be driven at a revolution of about 1800 rpm. The inertia force generated by a disc is in proportion to the radius of the disc to the fourth power. Furthermore, during the rotation, the video disc takes more windage loss than the digital audio disc. Hence approximately 150 to 200 gf.multidot.cm (1.47 to 1.96 N.multidot.cm) more torque is necessary for rotating the video disc, though these may be ignored for rotating the digital audio disc. In short, a drive motor for use in the disc player for both audio and video discs is required to have a performance such that the drive motor generates about 40 times as much large torque as a motor for the digital audio disc, and such that the rotating characteristic of the drive motor is stable enough to drive the digital audio disc which must be driven much slower than the video disc. However, those drive motors which satisfy both the large torque and the stable rotating characteristic are so large that anyone of them potentially butts against a reproducing head of the disc player when the reproducing head is transferred in the vicinity of the drive motor. The reproducing head is a device for reading the signals recorded on an information carrier disc, and thus as shown in FIG. 2, the objective lens 15 of the reproducing head 16 must be radially transferred to the position directly under the inner periphery of the information area of the disc 17, that is, the position in close proximity to the turntable (8). The information area is an annular area on an information carrier disc where information signals are recorded. In case of the digital audio disc, the periphery of the information area locates at a radial distance of 25 mm from the center of the disc.
Another example is the problem arising with the turntable. The digital audio disc has a central aperture having a diameter of 15 mm, and an information area having an inner diameter of 50 mm. The video disc has a central aperture having a diameter of 35 mm, and an information area having an inner diameter of 110 mm. The central aperture is a circular hole which is utilized for positioning the disc on the turntable. According to the sizes of these diameters of the apertures and inner diameters of the information areas, the optimum diameter of a turntable for the audio disc is in the range of 15 to 33 mm, and that of the video disc is in the range of 35 to 83 mm. However, a turntable for both the audio and video discs must have a diameter larger than 35 mm. That is to say, the turntable of this size has a potential for causing physical and optical interferences between itself and the reproducing head when the reproducing head detects the inner periphery of the information area of the digital audio disc.
Still another example is the problem arising with the means for centering the discs on the turntable. In case of the conventional disc player in FIG. 1, the turntables 7 and 8 have circular mound portions 7a and 8a respectively for centering discs on them. The mound portion 7a has a large diameter suitable for fitting in the central aperture of the video disc, and the mound portion 8a has a relatively small diameter proper to fitting in the central aperture of the audio disc. However, it is not easy to provide two centering members having different diameters on a single turntable while maintaining the turntable capable of supporting the discs.